The applicant's invention is a method and apparatus for receiving information from telephone lines and more particularly a transceiver method and apparatus for receiving data from a plurality of data transmitters which are coupled to a plurality of telephone lines after interrogating the data transmitters.
The applicant's invention is particularly suited to be used in an automatic utility meter reading system of the type described in co-pending application, Ser. No. 543,372, filed Oct. 19, 1983, for a centerpoint AUTOMATIC METER READING SYSTEM. The applicant's invention is also particularly suited to be used to interrogate and receive data from a meter interface system of the type described in co-pending application, Ser. No. 502,201, filed June 8, 1983, for METER INTERFACE UNIT FOR UTILITY METER READNG SYSTEM.
There have been other systems for receiving data from telephone lines such as one described in U.S. Pat. Reissue No. 26,331 to Dumont et al. Systems of the type of the Dumont invention use the telephone company's leakage testing system to call up individual meter installations. Once a meter installation is called up, it sends the meter information over the telephone line to a central telephone office. However, systems of the type typified by the Dumont invention have several disadvantages which make this type of system undesirable for its intended use.
First, such systems require the use of a telephone company's leakage testing system to be operable and such leakage testing systems can change, requiring an additional large investment in new equipment configured to the new leakage testing system. As well, not all telephone companies have the same type of leakage testing equipment, so that numerous configuations of the meter reading system must be devised to fit the numerous types of leakage testing equipment.
Second, such systems require a power supply, powered either from the power available at the meter installation site or from battery power, for each of its meter installations. This requirement of a power supply makes such systems costly, difficult to service, and makes the systems prone to failures due to common power outages at the installation site.
Third, such systems require a complex synchronous data output on the telephone line. The synchronous output requires that the meter installations send additional sync data over the telephone line. In the event that either the synchronizing data or synchronous meter data is momentarily interrupted by even a short noise pulse, which are quite common on telephone lines, the meter data will be lost.
Another type of system which has been used to send data over a telephone line is found in U.S. Pat. No. 3,922,490 to Pettis. The Pettis invention is a direct current system where several resistances are switched across tip and ring of the telephone line. The current drawn by the several different combinations of resistances connected to the telephone line are sensed at a central telephone office and any of several conditions are thus communicated. Typically, in systems represented by the Pettis invention, the least significant digit pointer of a utility meter makes or breaks a switch depending in which half of its rotation the pointer is presented located. The making or breaking of the switch causes the resistance across the telephone line to change. This change is sensed at the central office and the cumulative count of changes or transitions are totaled and the meter reading determined therefrom.
Of course, the Pettis invention, being a D.C. system, does not relate at all to the applicant's invention which is an alternating current transceiver for receiving data from a plurality of telephone lines.
U.S. Pat. No. 4,180,709 to Cosgrove et al, owned by the assignee of this invention, also describes a system for enabling the monitoring of a plurality of resistances placed across the D.C. telephone line. As with U.S. Pat. No. 3,922,490, this invention relates only to monitoring data conducted by D.C. current changes and does not relate at all to the applicant's invention which monitors A.C. signals from the telephone line.
None of the art described has been able to continuously monitor each of a plurality of telephone lines with a low impedance to the A.C. data signals sent and received without risking damage to the transceiver or the telephone lines; none of the art described has been able to receive data from data transmitters which are powered from the telephone line; and, none of the art described has been able to receive A.C. data which is asynchronous.
Likewise, none of the prior art systems have provisions for automatic compensation for variations in each of the line charcteristics.
None of the prior art systems include provisions for operating to receive utility data on an unterminated telephone line.
Further, none of the prior art systems are capable of commencing simultaneously with a number of closely associated pairs of telephone lines at levels adequate for reliable data communication but low enough to prevent interference.